#define _CRT_SECURE_NO_WARNINGS  1

#include<stdio.h>

#define N 10

int bin_search(int arr[], int left, int right, int k)
{
	if (left <= right)
	{
		int mid = (left + right) / 2;
		if (arr[mid] == k)return mid;
		if (k < arr[mid])return bin_search(arr, left, mid - 1, k);
		if (k > arr[mid])return bin_search(arr, mid + 1, right, k);
	}
	else
		return -1;
}


int main()
{
	int arr[N] = { 1,2,3,4,5,6,7,8,9,11 };
	int n = 0;
	scanf("%d", &n);
	int m=0;
	m = bin_search(arr, N - N, N - 1, n);
	printf("%d\n", m);
	return 0;
}

